1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a method of fabricating the liquid crystal display device. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for improving the quality of picture image.
2. Discussion of the Related Art
A CRT(cathode ray tube) display device has been widely used for televisions or personal computers. With the advent of modern information era, display devices have been required for larger screen size and smaller total volume of the device. However, the CRT is not an appropriate device to follow the trend because it requires a minimum distance between a screen and an electron gun. Thus, the CRT cannot be applied to small size and lower power consumption electronics such as wall-mounted televisions, portable televisions, and notebook computers.
For small size and low power consumption display devices, flat panel display devices such as LCD(Liquid Crystal Display), PDP(Plasma Display Panel), ELD (Electroluminescent Display), and VFD(Vacuum Fluorescent Display) have been introduced throughout the industries. Among the flat panel display devices, the LCD has been most widely researched device because it provides good picture quality and low power consumption in spite of various disadvantages.
There are two types of LCD; a passive matrix driving LCD and an active matrix driving LCD(hereinafter "AMLCD"). The AMLCD has been in more demand recently because a switching element is capable of independently operating each pixel for a high contrast ratio and a high resolution by minimizing a interference from neighboring pixels.
FIG. 1 is a plan view of a conventional AMLCD. As shown in FIG. 1, a gate bus line 1 and a data bus line 2 are crossing each other to define the pixel region. A thin film transistor (TFT) having a gate electrode 3 and source/drain electrodes 4 are disposed near the respective crossings of the gate bus line 1 and the data bus line 2. When the voltage is applied to the data bus line 2 through a data driving circuit of the liquid crystal panel, the TFT is operated and the signal is applied to the pixel electrode in the pixel region from the gate driving circuit.
An image representation region is the pixel region having a pixel electrode 5. Thus, a light shielding layer 6 must be formed to prevent the leakage of light through the gate bus line 1, the data bus line 2, and the TFT. The light shielding layer 6 is generally formed on a color filter substrate. In this case, however, there is a significant problem as set forth below. If the light shielding layer 6 on the color filter substrate does not correctly cover the gate bus line 1, the data bus line 2, and the TFT, the light leaks through these regions, so that the image quality is deteriorated. Moreover, if the light shielding layer 6 is extended so that the shielding layer 6 overlaps the pixel electrode 5 for preventing the light leakage, an aperture ratio becomes small.
In order to solve the problem, the light shielding layer 6 is directly formed on the gate bus line 1, the data bus line 2, and the TFT in the conventional LCD device as shown in FIG. 2. The gate electrode 3 and the gate insulating layer 11 are formed on the substrate 10. A semiconductor layer 13 is deposited on the gate insulating layer 11 and the source/drain electrodes 4 are formed thereon. Subsequently, a pixel electrode 5 contacting one of the source/drain electrodes 4 is formed on the pixel region. A passivation layer 16 is deposited over the pixel electrode 5 and the source/drain electrode 4.
Thereafter, the light shielding layer 6 is formed on the passivation layer 16 in the gate bus line 1, the data bus line 2, and the TFT region. An alignment layer 18 is then formed on the entire surface over the substrate 10. The light shielding layer 6 in this process is made of black resin, while the light shielding layer formed on the color filter substrate is made of metals such as Cr and CrOx. Since the light shielding layer 6 is directly formed on the gate bus line 1, the gate bus line 2, and TFT, the leakage of the light through these regions is prevented. Although a portion of the light shielding layer 6 of FIG. 2 is overlapped with the pixel electrode 5, the overlapped portion is very small, so that the aperture ratio is not much decreased.
Nonetheless, there is still a problem in the LCD of FIG. 2 as set forth below. When the substrate 10 is rubbed with a rubbing cloth to align the liquid crystal molecules, a portion of the pixel region is not rubbed completely due to a step H of the light shielding layer 6. As a result, the liquid crystal molecules in the portion L are not aligned properly. Although the liquid crystal molecules should be aligned in a predetermined direction along the rubbing direction, the liquid crystal molecules in the portion L are randomly aligned irrespective of the rubbing direction. Thus, the declination of the light occurs at the boundary between the aligned region and the non-aligned region due to the leakage of the light. The declination of the light is one of the main factors deteriorating the image quality of the LCD.
In order to solve this problem, a LCD structure shown in FIG. 3 is disclosed in U.S. Pat. No. 5,345,324. The structure of the LCD is similar to the conventional LCD shown in FIG. 2 except for an opaque metal layer 44 on a pixel electrode 35 below a non-aligned region L. A passivation layer 46 is deposited on the opaque metal layer 44 and a light shielding layer 36 is formed thereon. Thus, the opaque metal layer 44 shields the leakage of light through the region L and prevents the declination of the light on the screen caused by a step H of the light shielding layer 36. In this structure, however, the light shielding layer 36 decreases an image representation region so that the aperture ratio is also decreased.